Refrigerant compressor and freezer including same

ABSTRACT

A refrigerant compressor includes: an electric component (106); a compression component (107) driven by the electric component to compress a refrigerant; and a sealed container (101) accommodating the electric component and the compression component. The compression component includes: a shaft part (109, 110) rotated by the electric component; and a bearing part (114, 119) slidingly contacting the shaft part such that the shaft part is rotatable. A film (160) having hardness equal to or more than hardness of a sliding surface of the bearing part is provided on a sliding surface of the shaft part. Surface roughness of the sliding surface of the bearing part is smaller than surface roughness of the sliding surface of the shaft part.

TECHNICAL FIELD

The present invention relates to a refrigerant compressor for use in arefrigerator, an air conditioner, and the like, and a freezer includingthe refrigerant compressor.

BACKGROUND ART

In order to reduce the use of fossil fuels from the viewpoint of theprotection of the global environment, highly efficient refrigerantcompressors have been developed in recent years. Therefore, according toa sealed compressor of PTL 1, cast iron subjected to an insoluble filmtreatment using, for example, manganese phosphate is used as one ofsliding surfaces of a compression machine, and carbon steel is used asthe other sliding surface. According to a rotary compressor of PTL 2, aniron-based sintered alloy subjected to a soft-nitriding treatment isused as at least one of a roller and a vane plate which slide on eachother.

CITATION LIST Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 7-238885

PTL 2: Japanese Examined Patent Application Publication No. 55-4958

SUMMARY OF INVENTION Technical Problem

For example, a typical refrigerant compressor shown in FIG. 10 includessliding members, such as a main shaft 8 that rotates and a main bearing14 supporting the main shaft 8. When the main shaft 8 starts rotatingrelative to the main bearing 14, large frictional resistance force isgenerated between the main shaft 8 and the main bearing 14. Further, inrecent years, in order to improve the efficiency of the refrigerantcompressor, the viscosity of lubricating oil 2 supplied between thesliding surfaces is lowered, and the dimensions of the sliding surfacesare shortened. Thus, lubrication conditions are becoming severe.Therefore, for example, even when the manganese phosphate-based film isprovided on the sliding surface as in PTL 1, the film quickly abrades,and an input to the refrigerant compressor becomes high. On thisaccount, the efficiency of the refrigerant compressor deteriorates.

Further, in order to improve the efficiency of the refrigerantcompressor, the reduction in speed (for example, less than 20 Hz) byinverter drive is being promoted in recent years. Under suchcircumstances, an oil film between the sliding surfaces becomes thin, sothat contact between the sliding surfaces by a large number of minuteprojections on the surfaces frequently occurs, and the input to therefrigerant compressor becomes high. Further, for example, when the hardsoft-nitriding-treated film is provided on the sliding surface as in PTL2, the film coats the projections on the sliding surface, so that theprogress of the abrasion of the projections slows down, and the highinput state continues for a long period of time. Thus, the efficiency ofthe refrigerant compressor deteriorates.

The present invention was made in light of these, and an object of thepresent invention is to provide a refrigerant compressor whoseefficiency is prevented from deteriorating, and a freezer including therefrigerant compressor.

Solution to Problem

To achieve the above object, a refrigerant compressor according to thepresent invention includes: an electric component; a compressioncomponent driven by the electric component to compress a refrigerant;and a sealed container accommodating the electric component and thecompression component. The compression component includes a shaft partrotated by the electric component and a bearing part slidinglycontacting the shaft part such that the shaft part is rotatable. A filmhaving hardness equal to or more than hardness of a sliding surface ofthe bearing part is provided on a sliding surface of the shaft part.Surface roughness of the sliding surface of the bearing part is smallerthan surface roughness of the sliding surface of the shaft part.

A freezer according to the present invention includes: a heat radiator;a decompressor; a heat absorber; and the above refrigerant compressor.

Advantageous Effects of Invention

By the above configurations, the present invention can provide therefrigerant compressor whose efficiency is prevented from deteriorating,and the freezer including the refrigerant compressor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a refrigerant compressor according toEmbodiment 1.

FIG. 2 is a SIM image showing one example of an observation result of anoxide film by a SIM (scanning ion microscope), the oxide film being usedin the refrigerant compressor of FIG. 1.

FIG. 3 is a graph showing hardness of a main shaft of FIG. 1 in a depthdirection and hardness of a main bearing of FIG. 1 in the depthdirection.

FIG. 4A is a graph showing a curved line of a time-series change of aninput to the refrigerant compressor of FIG. 1.

FIG. 4B is a graph showing a curved line of a time-series change of aCOP of the refrigerant compressor of FIG. 1.

FIG. 5 is a diagram for explaining a compressive load in the refrigerantcompressor of FIG. 1.

FIG. 6 is a sectional view showing a sliding surface of the main bearingand a sliding surface of the main shaft in a direction perpendicular toa central axis of the main bearing, each sliding surface being notprovided with a surface roughness improved range.

FIG. 7 is a sectional view showing the sliding surface of the mainbearing and the sliding surface of the main shaft in a directionperpendicular to the central axis of the main bearing of FIG. 1.

FIG. 8 is a sectional view showing the sliding surface of the mainbearing and the sliding surface of the main shaft in a directionparallel to the central axis of the main bearing of FIG. 1.

FIG. 9 is a sectional view schematically showing a freezer according toEmbodiment 2.

FIG. 10 is a sectional view showing a conventional refrigerantcompressor.

DESCRIPTION OF EMBODIMENTS

A refrigerant compressor according to a first aspect of the presentinvention includes: an electric component; a compression componentdriven by the electric component to compress a refrigerant; and a sealedcontainer accommodating the electric component and the compressioncomponent. The compression component includes a shaft part rotated bythe electric component and a bearing part slidingly contacting the shaftpart such that the shaft part is rotatable. A film having hardness equalto or more than hardness of a sliding surface of the bearing part isprovided on a sliding surface of the shaft part. Surface roughness ofthe sliding surface of the bearing part is smaller than surfaceroughness of the sliding surface of the shaft part.

With this, the abrasion resistance of the sliding member can beimproved. In addition, even if the oil film is thin, the occurrence ofthe solid contact by the projections can be reduced. Therefore, therefrigerant compressor whose efficiency is prevented from deterioratingcan be provided.

The refrigerant compressor according to a second aspect of the presentinvention may be configured such that in the refrigerant compressoraccording to the first aspect, the surface roughness of at least a partof the sliding surface of the bearing part is smaller than the surfaceroughness of the sliding surface of the shaft part. With this, theoccurrence of the solid contact by the projections can be reduced, andthe productivity can be improved.

The refrigerant compressor according to a third aspect of the presentinvention may be configured such that in the refrigerant compressoraccording to the first or second aspect, a dimension of a range of thesliding surface of the bearing part is 1/10 or more and ½ or less of adimension of the sliding surface of the shaft part in a center axisdirection of the bearing part, the range having the surface roughnesssmaller than the surface roughness of the sliding surface of the shaftpart, and the range of the sliding surface of the bearing part is set atan end position of the bearing part in the center axis direction. Withthis, even if one-side hitting occurs between the shaft part and thebearing part, the occurrence of the solid contact by the projections canbe reduced, and the productivity can be improved.

The refrigerant compressor according to a fourth aspect of the presentinvention may be configured such that in the refrigerant compressoraccording to any one of the first to third aspects, arithmetic averageroughness Ra of a range of the sliding surface of the bearing part is0.01 μm or more and 0.2 μm or less, the range having the surfaceroughness smaller than the surface roughness of the sliding surface ofthe shaft part. With this, the occurrence of the solid contact by theprojections can be reduced, and the formation state of the oil film andthe productivity can be improved.

The refrigerant compressor according to a fifth aspect of the presentinvention may be configured such that in the refrigerant compressoraccording to any one of the first to fourth aspects, the electriccomponent is configured to be inverter-driven at a plurality ofoperation frequencies. With this, at the time of both a high-speedoperation in which the rotational frequency increases and a low-speedoperation in which the amount of oil supplied to each sliding surfacedecreases, the formation of the oil film can be promoted by the filmhaving excellent abrasion resistance and the action of easing acontacting/sliding state.

The freezer according to a sixth aspect of the present inventionincludes any one of the above sealed compressors. The energy saving ofthe freezer can be realized by the refrigerant compressor whoseefficiency is prevented from deteriorating.

Hereinafter, embodiments of the present invention will be explained withreference to the drawings. It should be noted that the present inventionis not limited to these embodiments.

Embodiment 1

Refrigerant Compressor

As shown in FIG. 1, the refrigerant compressor according to Embodiment 1includes a sealed container 101. The sealed container 101 is filled withR600a as refrigerant gas, and mineral oil as lubricating oil 103 isstored in a bottom portion of the sealed container 101.

The sealed container 101 accommodates an electric component 106 and acompression component 107. The electric component 106 includes a stator104 and a rotor 105 that rotates relative to the stator 104. Thecompression component 107 is a mechanism driven by the electriccomponent 106 to compress a refrigerant. The compression component 107is, for example, a reciprocating mechanism and includes a crank shaft108, a cylinder block 112, and a piston 132.

The compression component 107 includes the crank shaft 108, the cylinderblock 112, and the piston 132. The crank shaft 108 includes a main shaft109 and an eccentric shaft 110. The main shaft 109 is a shaft parthaving a columnar shape. A lower portion of the main shaft 109 ispress-fitted and fixed to the rotor 105. An oil supply pump 111communicating with the lubricating oil 103 is provided at a lower end ofthe main shaft 109. The eccentric shaft 110 is a shaft part having acolumnar shape and is arranged eccentrically with respect to the mainshaft 109.

The cylinder block 112 is made of, for example, an iron-based material,such as cast iron, and includes a cylinder bore 113 and a main bearing114. The cylinder bore 113 has a cylindrical shape and includes aninternal space. An end surface of the cylinder bore 113 is sealed by avalve plate 139.

The main bearing 114 is a bearing part having a cylindrical shape. Aninner peripheral surface of the main bearing 114 supports the main shaft109. The main bearing 114 is a journal bearing supporting a radial loadof the main shaft 109. Therefore, the inner peripheral surface of themain bearing 114 and an outer peripheral surface of the main shaft 109are opposed to each other, and the main shaft 109 slides on the innerperipheral surface of the main bearing 114. As above, a portion of theinner peripheral surface of the main bearing 114 and a portion of theouter peripheral surface of the main shaft 109 which portions slide oneach other are sliding surfaces. The main bearing 114 including thesliding surface and the main shaft 109 including the sliding surfaceconstitute a pair of sliding members.

One end portion of the piston 132 is inserted in the internal space ofthe cylinder bore 113 such that the piston 132 can reciprocate by therotation of the main shaft 109. With this, a compression chamber 134surrounded by the cylinder bore 113, the valve plate 139, and the piston132 is formed. A piston pin 115 is locked to a piston pin hole 116 ofthe other end portion of the piston 132 so as not to be rotatable, andthe other end portion of the piston 132 is coupled to one end portion ofa connecting rod (coupler) 117 by the piston pin 115. An eccentricbearing 119 is provided at the other end portion of the connecting rod117, and the eccentric shaft 110 supported by the eccentric bearing 119and the piston 132 are coupled to each other.

The eccentric bearing 119 is a bearing part having a cylindrical shape.An inner peripheral surface of the eccentric bearing 119 supports thecolumnar eccentric shaft 110 of the crank shaft 108. The eccentricbearing 119 is a journal bearing supporting a radial load of theeccentric shaft 110. Therefore, the inner peripheral surface of theeccentric bearing 119 and an outer peripheral surface of the eccentricshaft 110 are opposed to each other, and the eccentric shaft 110 slideson the inner peripheral surface of the eccentric bearing 119. A portionof the inner peripheral surface of the eccentric bearing 119 and aportion of the outer peripheral surface of the eccentric shaft 110 whichportions slide on each other are sliding surfaces. The eccentric bearing119 including the sliding surface and the eccentric shaft 110 includingthe sliding surface constitute a pair of sliding members.

A cylinder head 140 is fixed to the valve plate 139 at an opposite sideof the cylinder bore 113. The cylinder head 140 covers an ejection holeof the valve plate 139 to form a high-pressure chamber (not shown). Asuction tube (not shown) is fixed to the sealed container 101 andconnected to a low-pressure side (not shown) of a refrigeration cycle.The suction tube introduces the refrigerant gas from the refrigerationcycle into the sealed container 101. A suction muffler 142 is sandwichedbetween the valve plate 139 and the cylinder head 140.

Film

The main shaft 109 is constituted by a base member 150 and a filmcoating the surface of the base member 150. The base member 150 isformed by an iron-based material, such as gray cast iron (FC cast iron).The film constitutes, for example, the surface of the main shaft 109 andhas hardness equal to or more than hardness of the sliding surface ofthe main bearing 114. One example of the film is an oxide film 160. Forexample, the gray cast iron as the base member 150 is oxidized by usingknown oxidizing gas, such as carbon dioxide gas, and a known oxidationfacility at several hundreds of degrees Celsius (for example, 400 to800° C.). With this, the oxide film 160 can be formed on the surface ofthe base member 150.

FIG. 2 is an image (SIM image) when the main shaft 109 formed by coatingthe base member 150 with the oxide film 160 is observed with a SIM(scanning ion microscope). In FIG. 2, a protective film (resin film) forprotecting an observation sample is formed on a first portion 151. Adirection parallel to the surface of the oxide film 160 is referred toas a lateral direction, and a direction perpendicular to the surface ofthe oxide film 160 is referred to as a vertical direction.

The dimension (film thickness) of the oxide film 160 in the verticaldirection is about 3 μm. The oxide film 160 includes the first portion151, a second portion 152, and a third portion 153, and these portionsare laminated in this order from the surface toward the base member 150.This laminating direction is parallel to the vertical direction.

The first portion 151 constitutes the surface of the oxide film 160 andis formed on the second portion 152. The first portion 151 is formed bya structure of fine crystals. As a result of EDS (energy dispersiveX-ray spectrometry) and EELS (electron ray energy loss spectrometry), acomponent contained most in the first portion 151 is diiron trioxide(Fe₂O₃), and the first portion 151 also contains a silicon (Si)compound. The first portion 151 includes two portions (a first-a portion151 a and a first-b portion 151 b) which are different in crystaldensity from each other.

The first-a portion 151 a is formed on the first-b portion 151 b andconstitutes the surface of the oxide film 160. The crystal density ofthe first-a portion 151 a is lower than the crystal density of thefirst-b portion 151 b. The first-a portion 151 a contains gap portions158 (black portions in FIG. 2) and acicular structures 159 in someplaces. The acicular structures 159 are vertically long. For example, aminor-axis length of the acicular structure 159 in the verticaldirection is 100 nm or less, and a ratio (aspect ratio) obtained bydividing the length in the vertical direction by the length in thelateral direction is 1 or more and 10 or less.

The first-b portion 151 b is a structure formed by spreading finecrystals 155 having a particle diameter of 100 nm or less. Although thegap portions 158 and the acicular structures 159 are observed in thefirst-a portion 151 a, they are hardly observed in the first-b portion151 b.

The second portion 152 is formed on the third portion 153 and containsvertically long columnar structures 156. For example, the length of thecolumnar structure 156 in the vertical direction is about 100 nm or moreand 1 μm or less, and the length of the columnar structure 156 in thelateral direction is about 100 nm or more and 150 nm or less. The aspectratio of the columnar structure 156 is about 3 or more and 10 or less.According to the analytical results of the EDS and the EELS, a componentcontained most in the second portion 152 is triiron tetroxide (Fe₃O₄),and the second portion 152 also contains a silicon (Si) compound.

The third portion 153 is formed on the base member 150 and containslaterally long lamellar structures 157. For example, the length of thelamellar structure 157 in the vertical direction is several tens ofnanometers or less, and the length of the lamellar structure 157 in thelateral direction is about several hundreds of nanometers. The aspectratio of the lamellar structure 157 is 0.01 or more and 0.1 or less,i.e., the lamellar structure 157 is long in the lateral direction.According to the analytical results of the EDS and the EELS, a componentcontained most in the third portion 153 is triiron tetroxide (Fe₃O₄),and the third portion 153 also contains a silicon (Si) compound and asilicon (Si) solid solution component.

In FIG. 2, the oxide film 160 is constituted by the first portion 151,the second portion 152, and the third portion 153, and these first tothird portions 151 to 153 are laminated in this order. However, theconfiguration of the oxide film 160 and the order of the lamination arenot limited to these.

For example, the oxide film 160 may be constituted by a single layerthat is the first portion 151. The oxide film 160 may be constituted bytwo layers that are the first portion 151 and the second portion 152such that the first portion 151 forms the surface of the oxide film 160.The oxide film 160 may be constituted by two layers that are the firstportion 151 and the third portion 153 such that the first portion 151forms the surface of the oxide film 160.

The oxide film 160 may contain a composition other than the firstportion 151, the second portion 152, and the third portion 153. Theoxide film 160 may be constituted by four layers that are the firstportion 151, the second portion 152, the first portion 151, and thethird portion 153 such that the first portion 151 forms the surface ofthe oxide film 160.

The configuration of the oxide film 160 and the order of the laminationare easily realized by adjusting conditions. A typical condition is amethod of producing (forming) the oxide film 160. A known method ofoxidizing an iron-based material can be suitably used as the method ofproducing the oxide film 160. However, the present embodiment is notlimited to this. Conditions in the producing method are suitably set inaccordance with conditions, such as the type of the iron-based materialforming the base member 150, the surface state (for example, polishingfinish) of the base member 150, and a physical property of the desiredoxide film 160.

Operations of Refrigerant Compressor

Electric power supplied from a commercial power supply (not shown) issupplied to the electric component 106 through an external inverterdrive circuit (not shown). With this, the electric component 106 isinverter-driven at a plurality of operation frequencies, and the rotor105 of the electric component 106 rotates the crank shaft 108. Theeccentric motion of the eccentric shaft 110 of the crank shaft 108 isconverted into the linear motion of the piston 132 by the connecting rod117 and the piston pin 115, and the piston 132 reciprocates in thecompression chamber 134 of the cylinder bore 113. Therefore, therefrigerant gas introduced through the suction tube into the sealedcontainer 101 is sucked in the compression chamber 134 from the suctionmuffler 142. Then, the refrigerant gas is compressed in the compressionchamber 134 and ejected from the sealed container 101.

In accordance with the rotation of the crank shaft 108, the lubricatingoil 103 is supplied from the oil supply pump 111 to the sliding surfacesto lubricate the sliding surfaces. In addition, the lubricating oil 103forms a seal between the piston 132 and the cylinder bore 113 to sealthe compression chamber 134.

Hardness

FIG. 3 is a graph showing the hardness of the main shaft 109 in thedepth direction and the hardness of the main bearing 114 in the depthdirection. It should be noted that the hardness is shown by Vickershardness. A nano indentation apparatus (triboindenter) produced byScienta Omicron, Inc. is used for the measurement of the hardness.

Performed in the measurement of the hardness of the main shaft 109 is astep in which an indenter is pressed against the surface of the mainshaft 109 to apply a load to the surface for a certain period of time.Then, in the next step, the application of the load is stopped once, andthe indenter is again pressed against the surface of the main shaft 109to apply a load higher than the previous load to the surface for acertain period of time. Such steps in which the applied loads arestepwisely increased are repeatedly performed 15 times. Further, theloads in the respective steps are set such that the highest load becomes1 N. After each step, the hardness and depth of the oxide film 160 andthe hardness and depth of the base member 150 in the main shaft 109 aremeasured.

In the measurement of the hardness of the main bearing 114, a part ofthe main bearing 114 is cut by a fine cutter. The hardness of this partof the main bearing 114 is measured by applying a load of 0.5 kgf to theinner peripheral surface of the main bearing 114 by using the indenter.

As shown in FIG. 3, each of the hardness of the oxide film 160 and thehardness of the base member 150 in the main shaft 109 is equal to ormore than the hardness of the main bearing 114. As above, since thehardness of the main shaft 109 is made equal to or more than thehardness of the main bearing 114 by the oxide film 160, the abrasionresistance improves. In addition, the oil film between the pair ofsliding members is secured, and a highly-efficient operation in whichthe input to the refrigerant compressor is low from the initial stage ofthe operation is realized.

The hardness is one of mechanical properties of the surface of anobject, such as a substance or a material, or the vicinity of thesurface of the object. The hardness denotes the unlikelihood of thedeformation of the object and the unlikelihood of the damage of theobject when external force is applied to the object. Regarding thehardness, there are various measurement means (definitions) and theircorresponding values (measures of the hardness). Therefore, themeasurement means corresponding to a measurement target may be used.

For example, when the measurement target is a metal or a nonferrousmetal, an indentation hardness test method (such as the above-describednano indentation method, the Vickers hardness method, or the Rockwellhardness method) is used for the measurement.

Further, for the measurement targets, such as resin films and phosphatefilms, which are difficult to be measured by the indentation hardnesstest method, an abrasion test such as a ring-on-disk test is used. Inone example of this measurement method, a test piece is prepared byforming a film on the surface of a disk. With the test piece immersed inoil, the test piece is rotated at a rotational speed of 1 m/s for anhour while applying a load of 1000 N to the film by a ring. With this,the ring slides on the film. The state of the sliding surface of thefilm and the state of the sliding surface of the surface of the ring areobserved. As a result, it may be determined that one of the ring and thefilm which one is larger in abrasion loss has lower hardness.

Surface Roughness

As shown in FIG. 7, the surface roughness of the sliding surface of themain bearing 114 is smaller than the surface roughness of the slidingsurface of the main shaft 109. The surface roughness of the slidingsurface of the main shaft 109 corresponds to the surface roughness ofthe film of the main shaft 109.

As shown in FIG. 8, a range (surface roughness improved range 114 a)having the surface roughness smaller than the surface roughness of themain shaft 109 is provided at a part of a sliding surface 114 b of themain bearing 114. The surface roughness improved range 114 a is providedat an end position of the main bearing 114 in a center axis direction ofthe main bearing 114, and for example, is provided at an upper endportion of the sliding surface 114 b of the main bearing 114. However,the surface roughness improved range 114 a may be provided at a lowerend portion of the sliding surface 114 b of the main bearing 114.Therefore, the surface roughness improved range 114 a is only requiredto be provided at at least one of the upper end portion and lower endportion of the sliding surface 114 b of the main bearing 114.

The surface roughness improved range 114 a extends from an end (an upperend, a lower end) of the sliding surface 114 b of the main bearing 114in the center axis direction of the main bearing 114 and has a dimension(width) C. Further, the surface roughness improved range 114 a extendsover the entire periphery in the circumferential direction of the innerperipheral surface of the main bearing 114. The width C is 1/10 or moreand ½ or less of a dimension (width) D of the sliding surface 114 b ofthe main bearing 114. The sliding surface 114 b is a range of the innerperipheral surface of the main bearing 114 to which range the outerperipheral surface of the main shaft 109 is opposed and on which rangethe outer peripheral surface of the main shaft 109 slides. Therefore,for example, when a chamfered portion 114 c is provided on the innerperipheral surface of the main bearing 114, the chamfered portion 114 cis not included in the sliding surface 114 b. The sliding surface 114 bis not a portion where the main shaft 109 and the main bearing 114 slideon each other at all times but a portion where the main shaft 109 andthe main bearing 114 may slide on each other.

Even if one-side hitting occurs between the main shaft 109 and the mainbearing 114, the occurrence of solid contact by the minute projectionson the sliding surfaces can be reduced by the surface roughness improvedrange 114 a. In addition, since the small surface roughness portion(surface roughness improved range 114 a) which requires processing timeis small, the productivity can be improved.

If the width C of the surface roughness improved range 114 a is set toless than 1/10 of the width D, the oil film between the sliding surfaceof the main shaft 109 and the sliding surface of the main bearing 114cannot be kept, and the input to the refrigerant compressor increases.Further, even if the width C of the surface roughness improved range 114a is set to more than ½ of the width D, the input does not become lowerthan the input when the width C is set to ½ of the width D, and inaddition, the processing cost increases.

For example, arithmetic average roughness Ra of the surface roughnessimproved range 114 a is 0.01 μm or more and 0.2 μM or less. With this,the occurrence of the solid contact by the minute projections on thesliding surfaces can be reduced. In addition, the oil film between thesliding surfaces can be kept, and the productivity can be improved.

If the arithmetic average roughness Ra of the surface roughness improvedrange 114 a is larger than 0.2 μm, the oil film between the slidingsurfaces cannot be kept, and the input to the refrigerant compressorincreases. Further, even if the arithmetic average roughness Ra issmaller than 0.01 μm, the input does not decrease, and in addition, theprocessing cost increases. Thus, the productivity deteriorates.

As above, the surface roughness of the main bearing 114 is made smallerthan the surface roughness of the main shaft 109. With this, even whenthe surface of the main shaft 109 is made hard by the film, theimprovement of the abrasion resistance, the easing of the local contact,and the promotion of the formation of the oil film are realized betweenthe main shaft 109 and the main bearing 114. Therefore, thehighly-efficient refrigerant compressor can be provided, which is highin long-term reliability and in which the input to the refrigerantcompressor is low and stable from the initial stage of the operation.

Performance of Refrigerant Compressor

FIG. 4A shows a time-series change of the input to the refrigerantcompressor, and FIG. 4B shows a time-series change of a COP (Coefficientof Performance) of the refrigerant compressor. The COP is a coefficientused as an index of energy consumption efficiency of a refrigerantcompressor of a freezer/refrigerator or the like. The COP is a valueobtained by dividing a freezing capacity (W) by an input (W).

Herein, the input and the COP when the refrigerant compressor performsthe low-speed operation at the operation frequency of 17 Hz areobtained. Further, according to the refrigerant compressor of thepresent embodiment, the surface roughness of the main bearing 114 issmaller than the surface roughness of the main shaft 109. On the otherhand, according to a conventional refrigerant compressor, the surfaceroughness improved range 114 a is not provided at the main bearing 114.

As shown in FIG. 4A, in both the refrigerant compressor of the presentembodiment and the conventional refrigerant compressor, the inputimmediately after the operation start (hereinafter referred to as an“initial input”) is the highest. Then, the input gradually decreaseswith the lapse of the operating time and finally becomes a constantvalue (hereinafter referred to as a “steady input”) which changeslittle. Further, the initial input to the refrigerant compressor of thepresent embodiment is lower than that to the conventional refrigerantcompressor, and a time (transition time) it takes to change from theinitial input to the steady input in the refrigerant compressor of thepresent embodiment is shorter than that in the conventional refrigerantcompressor. A transition time t1 of the refrigerant compressor of thepresent embodiment is about ½ of a transition time t2 of theconventional refrigerant compressor. Thus, as shown in FIG. 4B, the COPof the refrigerant compressor of the present embodiment is stabilizedmore quickly and is improved more than that of the conventionalrefrigerant compressor.

This will be considered as below with reference to FIGS. 5 to 7. FIG. 5is an action diagram of a compressive load in the refrigerantcompressor. FIG. 6 is an enlarged view showing the sliding surface ofthe main bearing 114 and the sliding surface of the main shaft 109 inthe refrigerant compressor of the present embodiment before the surfaceroughness improved range 114 a is provided at the main bearing 114. FIG.7 is an enlarged view showing the sliding surface of the main bearing114 and the sliding surface of the main shaft 109 in the refrigerantcompressor of the present embodiment in which the surface roughnessimproved range 114 a is provided at the main bearing 114. By the surfaceroughness improved range 114 a, the surface roughness of the mainbearing 114 is made smaller than the surface roughness of the main shaft109.

The refrigerant compressor according to the present embodiment is areciprocating type, and pressure in the sealed container 101 is lowerthan a compressive load P in the compression chamber 134. Typically,with the compressive load P acting on the eccentric shaft 110, the mainshaft 109 connected to the eccentric shaft 110 is supported by thesingle main bearing 114 in a cantilever manner.

Therefore, as described in a literature (Collection of Papers of AnnualMeeting of The Japan Society of Mechanical Engineers, Vol. 5-1 (2005)page 143) written by Ito and others, the crank shaft 108 including themain shaft 109 and the eccentric shaft 110 whirls in an inclined statein the main bearing 114 by the influence of the compressive load P. Acomponent P1 of the compressive load P acts on the sliding surface ofthe main shaft 109 and the opposing sliding surface of the upper endportion of the main bearing 114. Further, a component P2 of thecompressive load P acts on the sliding surface of the main shaft 109 andthe opposing sliding surface of the lower end portion of the mainbearing 114. Thus, so-called one-side hitting occurs.

In FIG. 6, in the refrigerant compressor in which the surface roughnessimproved range 114 a is not provided, a large number of minuteprojections exist on both the sliding surface of the main shaft 109 andthe sliding surface of the main bearing 114. When the main shaft 109inclines in the main bearing 114, local contact occurs, and surfacepressure becomes high. Further, in the lower-speed operation, an oilfilm thickness h between the sliding surface of the main shaft 109 andthe sliding surface of the main bearing 114 decreases, and the solidcontact by the projections frequently occurs. In addition, when thesliding surface of the main shaft 109 is formed by the oxide film 160having high abrasion resistance, sliding marks are made on the slidingsurface of the main bearing 114 by the minute projections formed on thesurface of the main shaft 109 and having high hardness, and the time ofoccurrence of solid contact X increases. Therefore, the initial input tothe refrigerant compressor becomes high, and the transition time fromthe initial input to the steady input increases.

On the other hand, as shown in FIG. 7, in the refrigerant compressoraccording to the present embodiment, the surface roughness of thesliding surface of the main bearing 114 is made smaller than the surfaceroughness of the opposing sliding surface of the main shaft 109 by thesurface roughness improved range 114 a. With this, the solid contact bythe projections can be reduced, and the formation of the oil filmbetween the main shaft 109 and the main bearing 114 can be kept from theinitial stage of the operation. Therefore, the initial input can be madelow, and the transition time from the initial input to the steady inputcan be shortened. Further, since the oxide film 160 having high abrasionresistance is formed on the surface of the main shaft 109, thedurability can also be secured.

By the oxide film 160, the main shaft 109 becomes hard and obtainsimproved abrasion resistance. In addition, the attacking property(opponent attacking property) of the main shaft 109 with respect to themain bearing 114 is reduced, and the contact property of the main shaft109 at the initial stage of the sliding operation also improves.Therefore, in combination with the effect obtained by making the surfaceroughness of the main bearing 114 smaller than the surface roughness ofthe main shaft 109, the highly-efficient operation in which the input tothe refrigerant compressor is low from the initial stage of theoperation is realized.

Details of the increase in the abrasion resistance of the oxide film160, the reduction in the opponent attacking property of the oxide film160, and the improvement of the contact property of the oxide film 160at the initial stage of the sliding operation are described in JapanesePatent Application Nos. 2016-003910 and 2016-003909 filed by the presentapplicant. One of the reasons for these may be as below.

Since the oxide film 160 is an oxide of iron, the oxide film 160 ischemically more stable than the conventional phosphate film. Further,the film of the oxide of iron has higher hardness than the phosphatefilm. Therefore, by the formation of the oxide film 160 on the slidingsurface, the generation, adhesion, and the like of the abrasion powdercan be effectively prevented. As a result, the increase in the abrasionloss of the oxide film 160 itself can be effectively avoided, and theoxide film 160 exhibits high abrasion resistance.

In addition, as shown in FIG. 2, the first portion 151 of the oxide film160 contains the silicon (Si) compound having higher hardness than theoxide of iron. Since the surface of the oxide film 160 is constituted bythe first portion 151 containing the silicon (Si) compound, the oxidefilm 160 can exhibit higher abrasion resistance.

A component contained most in the first portion 151 constituting thesurface of the oxide film 160 is diiron trioxide (Fe₂O₃). The crystalstructure of diiron trioxide (Fe₂O₃) is rhombohedron, and the surface ofthe crystal structure of diiron trioxide (Fe₂O₃) is more flexible thanthe cubic crystal structure of triiron tetroxide (Fe₃O₄) located underthe crystal structure of diiron trioxide (Fe₂O₃) and the crystalstructures of a dense hexagonal crystal, face-centered cubic crystal,and body-centered tetragonal crystal of a nitriding film. Therefore, itis thought that the first portion 151 containing a large amount ofdiiron trioxide (Fe₂O₃) has more appropriate hardness, lower opponentattacking property, and better contact property at the initial stage ofthe sliding operation than a conventional gas nitriding film or atypical oxide film (triiron tetroxide (Fe₃O₄) film).

To be specific, the surface of the oxide film 160 constituting thesurface of the main shaft 109 contains a large amount of diiron trioxide(Fe₂O₃) that is relatively hard, has the rhombohedral crystal structure,and is flexible. Therefore, the opponent attacking property is reduced,and the shortage of the oil film and the like are prevented. Further,the contact property at the initial stage of the sliding operationimproves. In addition, in combination with the effect obtained by makingthe surface roughness of the main bearing 114 smaller than the surfaceroughness of the main shaft 109, the highly-efficient operation in whichthe input to the refrigerant compressor is low from the initial stage ofthe operation is realized.

Further, the second portion 152 and third portion 153 of the oxide film160 contain the silicon (Si) compound and are located between the firstportion 151 and the base member 150. Therefore, adhesive force of theoxide film 160 with respect to the base member 150 becomes strong. Inaddition, the amount of silicon contained in the third portion 153 islarger than that in the second portion 152. As above, the second portion152 containing the silicon (Si) compound and the third portion 153containing the silicon (Si) compound are laminated, and the thirdportion 153 containing a larger amount of silicon contacts the basemember 150. With this, the adhesive force of the oxide film 160 can befurther increased. As a result, the proof stress of the oxide film 160with respect to the load at the time of the sliding operation improves,and the abrasion resistance of the oxide film 160 further improves. Evenif the first portion 151 forming the surface of the oxide film 160abrades, the second portion 152 and the third portion 153 remain, sothat the oxide film 160 exhibits more excellent abrasion resistance.

Further, from a different point of view, it is thought that the increasein the abrasion resistance of the oxide film 160, the reduction in theopponent attacking property of the oxide film 160, and the improvementof the contact property of the oxide film 160 at the initial stage ofthe sliding operation are realized by the following reasons.

To be specific, the first portion 151 constituting the surface of theoxide film 160 contains the silicon (Si) compound, and in addition, hasa dense fine crystal structure. Therefore, the oxide film 160 exhibitshigh abrasion resistance.

The first portion 151 has the fine crystal structure, and the slightminute gap portions 158 are formed in some places among the finecrystals, or minute depressions and projections are formed on thesurface of the first portion 151. Therefore, the lubricating oil 103 iseasily held on the surface (sliding surface) of the oxide film 160 bycapillarity. To be specific, since there are the slight minute gapportions 158 and/or the minute depressions and projections, thelubricating oil 103 can be held on the sliding surfaces even under asevere sliding state, i.e., so-called “oil holding property” can beexhibited. As a result, the oil film is easily formed on the slidingsurface.

Further, in the oxide film 160, the columnar structures 156 (secondportion 152) and the lamellar structures 157 (third portion 153) existunder the first portion 151 and closer to the base member 150. Thesestructures are lower in hardness and softer than the fine crystals 155of the first portion 151. Therefore, during the sliding operation, thecolumnar structures 156 and the lamellar structures 157 serve as“cushioning materials.” With this, by the pressure applied to thesurface of the fine crystals 155 during the sliding operation, the finecrystals 155 behave so as to be compressed toward the base member 150.As a result, the opponent attacking property of the oxide film 160 issignificantly lower than that of the other surface treated films, andtherefore, the abrasion of the sliding surface of the opponent member iseffectively suppressed.

It should be noted that the function of the “cushioning materials” isexhibited even if only one of the second portion 152 and the thirdportion 153 is provided. Therefore, the second portion 152 or the thirdportion 153 is only required to be located under the first portion 151.It is preferable that both the second portion 152 and the third portion153 be located under the first portion 151.

The oxide film 160 has the low opponent attacking property and canexhibit the satisfactory “oil holding property.” Therefore, an oil filmforming ability of the shaft part including the oxide film 160significantly improves. By the high oil film forming ability incombination with the effect obtained by making the surface roughness ofthe bearing part small, the highly-efficient operation in which theinput to the refrigerant compressor is low from the initial stage of theoperation is realized.

MODIFIED EXAMPLE

According to the above configuration, the main shaft 109 is used as theshaft part, and the main bearing 114 is used as the bearing part.However, the shaft part and the bearing part are not limited to these.For example, the eccentric shaft 110 may be used as the shaft part, andthe eccentric bearing 119 may be used as the bearing part. Therefore, afilm having hardness equal to or more than the hardness of the opposingbearing part may be provided on the surface of the shaft part, i.e., onat least one of the surface of the main shaft 109 and the surface of theeccentric shaft 110. Further, the surface roughness of the bearing part,i.e., at least one of the surface roughness of the main bearing 114 andthe surface roughness of the eccentric bearing 119 may be made smallerthan the surface roughness of the opposing shaft part.

In all the above configurations, the oxide film 160 is included on thesurface of the shaft part. However, the film on the surface of the shaftpart is not limited to this as long as the film has hardness equal to ormore than the hardness of the bearing part. Examples of the film of theshaft part include a compound layer, a mechanical strength improvedlayer, and a layer formed by a coating method.

To be specific, when the base member 150 of the shaft part is aniron-based member, the film may be a film formed by a typical quenchingmethod and a method of impregnating a surface layer with carbon,nitrogen, or the like. Further, the film may be a film formed by anoxidation treatment using steam and an oxidation treatment of performingimmersion in a sodium hydroxide aqueous solution. Furthermore, the filmmay be a layer (mechanical strength improved layer) which is formed bycold working, work hardening, solute strengthening, precipitationstrengthening, dispersion strengthening, and grain refining and in whicha slip motion of a dislocation is suppressed, and the base member 150 isstrengthened. Further, the film may be a layer formed by a coatingmethod, such as plating, thermal spraying, PVD, or CVD.

In all the above configurations, the range (surface roughness improvedrange 114 a) having the surface roughness smaller than the surfaceroughness of the main shaft 109 is provided on a part of the slidingsurface of the main bearing 114. However, the surface roughness improvedrange 114 a on the sliding surface of the main bearing 114 is notlimited to this. The surface roughness improved range 114 a may beprovided on the entire sliding surface (entire sliding range) of themain bearing 114.

In all the above configurations, the iron-based material is used as thematerial of the base member 150 of the shaft part. However, a materialother than the iron-based material may be used as the material of thebase member 150 as long as a film having hardness equal to or more thanthe hardness of the bearing part can be formed.

In all the above configurations, the effects in the example in which therefrigerant compressor is driven by the low-speed operation (forexample, at the operation frequency of 17 Hz) are explained. However,the operation of the refrigerant compressor is not limited to this. Evenwhen the refrigerant compressor performs the operation at a commercialrotational frequency or the high-speed operation at a high rotationalfrequency, the performance and reliability of the refrigerant compressorcan be improved as with when the refrigerant compressor performs thelow-speed operation.

In all the above configurations, the refrigerant compressor is areciprocating type. However, the refrigerant compressor may be the othertype, such as a rotary type, a scroll type, or a vibration type.Further, the configuration in which (i) the shaft part includes the filmhaving the hardness equal to or more than the hardness of the bearingpart and (ii) the surface roughness of the bearing part is made smallerthan the surface roughness of the bearing part is not limited to therefrigerant compressor and may be used in an apparatus including slidingsurfaces, and with this, the same effects can be obtained. Examples ofthe apparatus including the sliding surfaces include a pump and a motor.

Embodiment 2

FIG. 9 is a schematic diagram showing a freezer according to Embodiment2. Herein, the basic configuration of the freezer will be schematicallyexplained.

In FIG. 9, the freezer includes a main body 301, a partition wall 307,and a refrigerant circuit 309. The main body 301 includes: aheat-insulation box body including an opening on one surface thereof;and a door body configured to open and close the opening. The partitionwall 307 divides the inside of the main body 301 into a storage space303 for articles and a machine room 305. The refrigerant circuit 309 isconfigured such that a refrigerant compressor 300, a heat radiator 313,a decompressor 315, and a heat absorber 317 are annularly connected toone another by pipes. The refrigerant circuit 309 cools the inside ofthe storage space 303.

The heat absorber 317 is arranged in the storage space 303 including ablower (not shown). As shown by arrows in FIG. 9, cooling air of theheat absorber 317 is stirred by the blower so as to circulate in thestorage space 303. Thus, the inside of the storage space 303 is cooled.

The freezer configured as above includes the refrigerant compressoraccording to Embodiment 1 as the refrigerant compressor 300. With this,the film of the shaft part, such as the main shaft 109, of therefrigerant compressor 300 has the hardness equal to or more than thehardness of the opposing bearing part such as the main bearing 114, andthe surface roughness of the bearing part is smaller than the surfaceroughness of the shaft part. Therefore, the improvement of the abrasionresistance, the reduction in the local contact/slide, and the keeping ofthe formation of the oil film are realized between the shaft part andthe bearing part. On this account, since the performance of the freezerimproves, the energy saving by the reduction in the power consumptioncan be realized, and the reliability can be improved.

The foregoing has explained the refrigerant compressor according to thepresent invention and the freezer including the refrigerant compressoraccording to the present invention based on the above embodiments.However, the present invention is not limited to these. To be specific,the embodiments disclosed herein are merely illustrative in all aspectsand should not be recognized as being restrictive. The scope of thepresent invention is defined by the scope of the claims, not by theabove description, and is intended to include meaning equivalent to thescope of the claims and all modifications within the scope.

INDUSTRIAL APPLICABILITY

As above, the present invention can provide a refrigerant compressorwhose efficiency is prevented from deteriorating, and a freezerincluding the refrigerant compressor. Therefore, the present inventionis widely applicable to various apparatuses using the refrigerationcycle.

REFERENCE SIGNS LIST

-   -   101 sealed container    -   106 electric component    -   107 compression component    -   109 main shaft (shaft part)    -   110 eccentric shaft (shaft part)    -   114 main bearing (bearing part)    -   119 eccentric bearing (bearing part)    -   160 oxide film (film)    -   300 refrigerant compressor

1. A refrigerant compressor comprising: an electric component; acompression component driven by the electric component to compress arefrigerant; and a sealed container accommodating the electric componentand the compression component, wherein: the compression componentincludes a shaft part rotated by the electric component and a bearingpart slidingly contacting the shaft part such that the shaft part isrotatable; a film having hardness equal to or more than hardness of asliding surface of the bearing part is provided on a sliding surface ofthe shaft part; and surface roughness of the sliding surface of thebearing part is smaller than surface roughness of the sliding surface ofthe shaft part.
 2. The refrigerant compressor according to claim 1,wherein the surface roughness of at least a part of the sliding surfaceof the bearing part is smaller than the surface roughness of the slidingsurface of the shaft part.
 3. The refrigerant compressor according toclaim 1, wherein: a dimension of a range of the sliding surface of thebearing part is 1/10 or more and ½ or less of a dimension of the slidingsurface of the shaft part in a center axis direction of the bearingpart, the range having the surface roughness smaller than the surfaceroughness of the sliding surface of the shaft part; and the range of thesliding surface of the bearing part is set at an end position of thebearing part in the center axis direction.
 4. The refrigerant compressoraccording to claim 1, wherein arithmetic average roughness Ra of a rangeof the sliding surface of the bearing part is 0.01 μm or more and 0.2 μmor less, the range having the surface roughness smaller than the surfaceroughness of the sliding surface of the shaft part.
 5. The refrigerantcompressor according to claim 1, wherein the electric component isconfigured to be inverter-driven at a plurality of operationfrequencies.
 6. A freezer comprising: a heat radiator; a decompressor; aheat absorber; and the refrigerant compressor according to claim 1.